Better performance on older version of GCC

Better performance on older version of GCC

[Corey Kasten]

Hello all,

I have two computers with two different versions of GCC. Otherwise the
two systems have identical hardware. I have a processor and memory
intensive benchmark program which I compile on both systems and I cannot
understand why the system with older GCC version compiles faster code. 

System A has GCC version "4.1.2 20070925 (Red Hat 4.1.2-33)"
System B has GCC version "4.3.0 20080428 (Red Hat 4.3.0-8)"

I find that the executable compiled on system A runs faster (on both
systems) than the executable compiled on system B (on both system), by a
factor about approximately 4 times. I have attempted to play with the
GCC optimizer flags and have not been able to get System B (with the
later GCC version) to compile code with any better performance. Could
someone please help figure this out?

Below is the GCC command I run on System A followed by the verbose
output:
gcc -v -Wall -DOFFLINE_WEIGHTS -DDOUBLEP -g bfbenchmark_threaded.c -lm
-lrt -lpthread -O3 -o bfbenchmark_threaded

---------------------------BEGIN OUTPUT---------------------------------
Using built-in specs.
Target: i386-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-languages=c,c++,objc,obj-c
++,java,fortran,ada --enable-java-awt=gtk --disable-dssi --enable-plugin
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --with-cpu=generic
--host=i386-redhat-linux
Thread model: posix
gcc version 4.1.2 20070925 (Red Hat 4.1.2-33)
 /usr/libexec/gcc/i386-redhat-linux/4.1.2/cc1 -quiet -v
-DOFFLINE_WEIGHTS -DDOUBLEP bfbenchmark_threaded.c -quiet -dumpbase
bfbenchmark_threaded.c -mtune=generic -auxbase bfbenchmark_threaded -g
-O3 -Wall -version -o /tmp/ccvxPCd0.s
ignoring nonexistent directory
"/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../i386-redhat-linux/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/lib/gcc/i386-redhat-linux/4.1.2/include
 /usr/include
End of search list.
GNU C version 4.1.2 20070925 (Red Hat 4.1.2-33) (i386-redhat-linux)
	compiled by GNU C version 4.1.2 20070925 (Red Hat 4.1.2-33).
GGC heuristics: --param ggc-min-expand=100 --param
ggc-min-heapsize=131072
Compiler executable checksum: ab322ce5b87a7c6c23d60970ec7b7b31
 as -V -Qy -o /tmp/ccU8kZL1.o /tmp/ccvxPCd0.s
GNU assembler version 2.17.50.0.18 (i386-redhat-linux) using BFD version
version 2.17.50.0.18-1 20070731
 /usr/libexec/gcc/i386-redhat-linux/4.1.2/collect2 --eh-frame-hdr
--build-id -m elf_i386 --hash-style=gnu
-dynamic-linker /lib/ld-linux.so.2 -o
bfbenchmark_threaded /usr/lib/gcc/i386-redhat-linux/4.1.2/../../../crt1.o /usr/lib/gcc/i386-redhat-linux/4.1.2/../../../crti.o /usr/lib/gcc/i386-redhat-linux/4.1.2/crtbegin.o -L/usr/lib/gcc/i386-redhat-linux/4.1.2 -L/usr/lib/gcc/i386-redhat-linux/4.1.2 -L/usr/lib/gcc/i386-redhat-linux/4.1.2/../../.. /tmp/ccU8kZL1.o -lm -lrt -lpthread -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/i386-redhat-linux/4.1.2/crtend.o /usr/lib/gcc/i386-redhat-linux/4.1.2/../../../crtn.o
---------------------------END OUTPUT---------------------------------



Below is the GCC command I run on System A followed by the verbose
output:
gcc -v -Wall -DOFFLINE_WEIGHTS -DDOUBLEP -g bfbenchmark_threaded.c -lm
-lrt -lpthread -O3 -o bfbenchmark_threaded

---------------------------BEGIN OUTPUT---------------------------------
Using built-in specs.
Target: i386-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info
--with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-bootstrap
--enable-shared --enable-threads=posix --enable-checking=release
--with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada
--enable-java-awt=gtk --disable-dssi --enable-plugin
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--disable-libjava-multilib --with-cpu=generic --build=i386-redhat-linux
Thread model: posix
gcc version 4.3.0 20080428 (Red Hat 4.3.0-8) (GCC) 
COLLECT_GCC_OPTIONS='-v' '-Wall' '-DOFFLINE_WEIGHTS' '-DDOUBLEP' '-g'
'-O3' '-o' 'bfbenchmark_threaded' '-mtune=generic'
 /usr/libexec/gcc/i386-redhat-linux/4.3.0/cc1 -quiet -v
-DOFFLINE_WEIGHTS -DDOUBLEP bfbenchmark_threaded.c -quiet -dumpbase
bfbenchmark_threaded.c -mtune=generic -auxbase bfbenchmark_threaded -g
-O3 -Wall -version -o /tmp/ccB4B5PI.s
ignoring nonexistent directory
"/usr/lib/gcc/i386-redhat-linux/4.3.0/include-fixed"
ignoring nonexistent directory
"/usr/lib/gcc/i386-redhat-linux/4.3.0/../../../../i386-redhat-linux/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/lib/gcc/i386-redhat-linux/4.3.0/include
 /usr/include
End of search list.
GNU C (GCC) version 4.3.0 20080428 (Red Hat 4.3.0-8) (i386-redhat-linux)
	compiled by GNU C version 4.3.0 20080428 (Red Hat 4.3.0-8), GMP version
4.2.2, MPFR version 2.3.0-p2.
GGC heuristics: --param ggc-min-expand=100 --param
ggc-min-heapsize=131072
Compiler executable checksum: a6100d27c113f078654b8bcf6e8eb1d2
COLLECT_GCC_OPTIONS='-v' '-Wall' '-DOFFLINE_WEIGHTS' '-DDOUBLEP' '-g'
'-O3' '-o' 'bfbenchmark_threaded' '-mtune=generic'
 as -V -Qy -o /tmp/ccoiU9Dv.o /tmp/ccB4B5PI.s
GNU assembler version 2.18.50.0.6 (i386-redhat-linux) using BFD version
version 2.18.50.0.6-2 20080403
COMPILER_PATH=/usr/libexec/gcc/i386-redhat-linux/4.3.0/:/usr/libexec/gcc/i386-redhat-linux/4.3.0/:/usr/libexec/gcc/i386-redhat-linux/:/usr/lib/gcc/i386-redhat-linux/4.3.0/:/usr/lib/gcc/i386-redhat-linux/:/usr/libexec/gcc/i386-redhat-linux/4.3.0/:/usr/libexec/gcc/i386-redhat-linux/:/usr/lib/gcc/i386-redhat-linux/4.3.0/:/usr/lib/gcc/i386-redhat-linux/
LIBRARY_PATH=/usr/lib/gcc/i386-redhat-linux/4.3.0/:/usr/lib/gcc/i386-redhat-linux/4.3.0/:/usr/lib/gcc/i386-redhat-linux/4.3.0/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-Wall' '-DOFFLINE_WEIGHTS' '-DDOUBLEP' '-g'
'-O3' '-o' 'bfbenchmark_threaded' '-mtune=generic'
 /usr/libexec/gcc/i386-redhat-linux/4.3.0/collect2 --eh-frame-hdr
--build-id -m elf_i386 --hash-style=gnu
-dynamic-linker /lib/ld-linux.so.2 -o
bfbenchmark_threaded /usr/lib/gcc/i386-redhat-linux/4.3.0/../../../crt1.o /usr/lib/gcc/i386-redhat-linux/4.3.0/../../../crti.o /usr/lib/gcc/i386-redhat-linux/4.3.0/crtbegin.o -L/usr/lib/gcc/i386-redhat-linux/4.3.0 -L/usr/lib/gcc/i386-redhat-linux/4.3.0 -L/usr/lib/gcc/i386-redhat-linux/4.3.0/../../.. /tmp/ccoiU9Dv.o -lm -lrt -lpthread -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/i386-redhat-linux/4.3.0/crtend.o /usr/lib/gcc/i386-redhat-linux/4.3.0/../../../crtn.o

---------------------------END OUTPUT---------------------------------

Thanks in advance for your help,

Corey

Re: Better performance on older version of GCC

[H.J. Lu]

On Fri, Aug 27, 2010 at 6:44 AM, Corey Kasten
<corey@materialintelligencellc.com> wrote:
> Hello all,
>
> I have two computers with two different versions of GCC. Otherwise the
> two systems have identical hardware. I have a processor and memory
> intensive benchmark program which I compile on both systems and I cannot
> understand why the system with older GCC version compiles faster code.
>
> System A has GCC version "4.1.2 20070925 (Red Hat 4.1.2-33)"
> System B has GCC version "4.3.0 20080428 (Red Hat 4.3.0-8)"
>
> I find that the executable compiled on system A runs faster (on both
> systems) than the executable compiled on system B (on both system), by a
> factor about approximately 4 times. I have attempted to play with the
> GCC optimizer flags and have not been able to get System B (with the
> later GCC version) to compile code with any better performance. Could
> someone please help figure this out?
>

Can you try gcc 4.5.1?

-- 
H.J.

Re: Better performance on older version of GCC

[Nathan Froyd]

On Fri, Aug 27, 2010 at 09:44:25AM -0400, Corey Kasten wrote:
> I find that the executable compiled on system A runs faster (on both
> systems) than the executable compiled on system B (on both system), by a
> factor about approximately 4 times. I have attempted to play with the
> GCC optimizer flags and have not been able to get System B (with the
> later GCC version) to compile code with any better performance. Could
> someone please help figure this out?

It's almost impossible to tell what's going on without an actual
testcase.  You might not be able to provide the actual code, but you
could try distilling it down to something you could release.

-Nathan

Re: Better performance on older version of GCC

[Corey Kasten]

[-- Attachment #1: Type: text/plain, Size: 1113 bytes --]

On Fri, 2010-08-27 at 06:50 -0700, Nathan Froyd wrote:
> On Fri, Aug 27, 2010 at 09:44:25AM -0400, Corey Kasten wrote:
> > I find that the executable compiled on system A runs faster (on both
> > systems) than the executable compiled on system B (on both system), by a
> > factor about approximately 4 times. I have attempted to play with the
> > GCC optimizer flags and have not been able to get System B (with the
> > later GCC version) to compile code with any better performance. Could
> > someone please help figure this out?
> 
> It's almost impossible to tell what's going on without an actual
> testcase.  You might not be able to provide the actual code, but you
> could try distilling it down to something you could release.
> 
> -Nathan

Thanks for the reply Nathan.

I have attached an archive with the test case code. The code is built by
build.sh and outputs the number of microseconds to complete the
processing.

Compiling with GCC version "4.1.2 20070925 (Red Hat 4.1.2-33)" produces
code that runs in about 66% of the time than does GCC version "4.3.0
20080428 (Red Hat 4.3.0-8)"

Thanks

Corey

[-- Attachment #2: testbenchmark.100827.1050.tgz --]
[-- Type: application/x-compressed-tar, Size: 5022 bytes --]

Re: Better performance on older version of GCC

[Richard Guenther]

On Fri, Aug 27, 2010 at 5:02 PM, Corey Kasten
<corey@materialintelligencellc.com> wrote:
> On Fri, 2010-08-27 at 06:50 -0700, Nathan Froyd wrote:
>> On Fri, Aug 27, 2010 at 09:44:25AM -0400, Corey Kasten wrote:
>> > I find that the executable compiled on system A runs faster (on both
>> > systems) than the executable compiled on system B (on both system), by a
>> > factor about approximately 4 times. I have attempted to play with the
>> > GCC optimizer flags and have not been able to get System B (with the
>> > later GCC version) to compile code with any better performance. Could
>> > someone please help figure this out?
>>
>> It's almost impossible to tell what's going on without an actual
>> testcase.  You might not be able to provide the actual code, but you
>> could try distilling it down to something you could release.
>>
>> -Nathan
>
> Thanks for the reply Nathan.
>
> I have attached an archive with the test case code. The code is built by
> build.sh and outputs the number of microseconds to complete the
> processing.
>
> Compiling with GCC version "4.1.2 20070925 (Red Hat 4.1.2-33)" produces
> code that runs in about 66% of the time than does GCC version "4.3.0
> 20080428 (Red Hat 4.3.0-8)"

-fcx-limited-range or -fcx-fortran-rules.  4.3 now is more conforming than 4.1.

Richard.

> Thanks
>
> Corey
>

Re: Better performance on older version of GCC

[Corey Kasten]

On Fri, 2010-08-27 at 17:09 +0200, Richard Guenther wrote:
> On Fri, Aug 27, 2010 at 5:02 PM, Corey Kasten
> <corey@materialintelligencellc.com> wrote:
> > On Fri, 2010-08-27 at 06:50 -0700, Nathan Froyd wrote:
> >> On Fri, Aug 27, 2010 at 09:44:25AM -0400, Corey Kasten wrote:
> >> > I find that the executable compiled on system A runs faster (on both
> >> > systems) than the executable compiled on system B (on both system), by a
> >> > factor about approximately 4 times. I have attempted to play with the
> >> > GCC optimizer flags and have not been able to get System B (with the
> >> > later GCC version) to compile code with any better performance. Could
> >> > someone please help figure this out?
> >>
> >> It's almost impossible to tell what's going on without an actual
> >> testcase.  You might not be able to provide the actual code, but you
> >> could try distilling it down to something you could release.
> >>
> >> -Nathan
> >
> > Thanks for the reply Nathan.
> >
> > I have attached an archive with the test case code. The code is built by
> > build.sh and outputs the number of microseconds to complete the
> > processing.
> >
> > Compiling with GCC version "4.1.2 20070925 (Red Hat 4.1.2-33)" produces
> > code that runs in about 66% of the time than does GCC version "4.3.0
> > 20080428 (Red Hat 4.3.0-8)"
> 
> -fcx-limited-range or -fcx-fortran-rules.  4.3 now is more conforming than 4.1.
> 
> Richard.
> 
> > Thanks
> >
> > Corey
> >

Richard,

-fcx-limited-range worked great on both my real benchmark and my test
achive. GCC didn't recognize -fcx-fortran-rules, but obviously I don't
need it.

Thanks so much,
Corey

  

Re: Better performance on older version of GCC

[Xinliang David Li]

Briefly looked at it -- the trunk gcc also regresses a lot compared to
the binary you attached. (To match your binary, also added
-mfpmath=387 -m32 options)

Two problems:

1) more register spills in the trunk version -- the old compiler seems
more effective in using fp stack registers;
2) the complex multiplication -- the old version emits inline sequence
while the trunk version emits call to _muld3c intrinsinc.

You can probably file a bug report on this.

Thanks,

David

On Fri, Aug 27, 2010 at 8:39 AM, Corey Kasten
<corey@materialintelligencellc.com> wrote:
> On Fri, 2010-08-27 at 17:09 +0200, Richard Guenther wrote:
>> On Fri, Aug 27, 2010 at 5:02 PM, Corey Kasten
>> <corey@materialintelligencellc.com> wrote:
>> > On Fri, 2010-08-27 at 06:50 -0700, Nathan Froyd wrote:
>> >> On Fri, Aug 27, 2010 at 09:44:25AM -0400, Corey Kasten wrote:
>> >> > I find that the executable compiled on system A runs faster (on both
>> >> > systems) than the executable compiled on system B (on both system), by a
>> >> > factor about approximately 4 times. I have attempted to play with the
>> >> > GCC optimizer flags and have not been able to get System B (with the
>> >> > later GCC version) to compile code with any better performance. Could
>> >> > someone please help figure this out?
>> >>
>> >> It's almost impossible to tell what's going on without an actual
>> >> testcase.  You might not be able to provide the actual code, but you
>> >> could try distilling it down to something you could release.
>> >>
>> >> -Nathan
>> >
>> > Thanks for the reply Nathan.
>> >
>> > I have attached an archive with the test case code. The code is built by
>> > build.sh and outputs the number of microseconds to complete the
>> > processing.
>> >
>> > Compiling with GCC version "4.1.2 20070925 (Red Hat 4.1.2-33)" produces
>> > code that runs in about 66% of the time than does GCC version "4.3.0
>> > 20080428 (Red Hat 4.3.0-8)"
>>
>> -fcx-limited-range or -fcx-fortran-rules.  4.3 now is more conforming than 4.1.
>>
>> Richard.
>>
>> > Thanks
>> >
>> > Corey
>> >
>
> Richard,
>
> -fcx-limited-range worked great on both my real benchmark and my test
> achive. GCC didn't recognize -fcx-fortran-rules, but obviously I don't
> need it.
>
> Thanks so much,
> Corey
>
>
>
>

Re: Better performance on older version of GCC

[Andrew Pinski]

On Fri, Aug 27, 2010 at 5:12 PM, Xinliang David Li <davidxl@google.com> wrote:
> Briefly looked at it -- the trunk gcc also regresses a lot compared to
> the binary you attached. (To match your binary, also added
> -mfpmath=387 -m32 options)
>
> Two problems:
>
> 1) more register spills in the trunk version -- the old compiler seems
> more effective in using fp stack registers;
> 2) the complex multiplication -- the old version emits inline sequence
> while the trunk version emits call to _muld3c intrinsinc.

Neither of these seems like real bug reportable ones.  The first one
is that due to -fexcess-precision=standard being default in 4.5 and
above (see PR 323).  The second one is due to -fcx-limited-range not
being default any more (I cannot remember the bug number which changed
that though).

Thanks,
Andrew Pinski

Re: Better performance on older version of GCC

[Xinliang David Li]

Right -- I missed Richard's previous email regarding the options.

Thanks,

David

On Fri, Aug 27, 2010 at 5:21 PM, Andrew Pinski <pinskia@gmail.com> wrote:
> On Fri, Aug 27, 2010 at 5:12 PM, Xinliang David Li <davidxl@google.com> wrote:
>> Briefly looked at it -- the trunk gcc also regresses a lot compared to
>> the binary you attached. (To match your binary, also added
>> -mfpmath=387 -m32 options)
>>
>> Two problems:
>>
>> 1) more register spills in the trunk version -- the old compiler seems
>> more effective in using fp stack registers;
>> 2) the complex multiplication -- the old version emits inline sequence
>> while the trunk version emits call to _muld3c intrinsinc.
>
> Neither of these seems like real bug reportable ones.  The first one
> is that due to -fexcess-precision=standard being default in 4.5 and
> above (see PR 323).  The second one is due to -fcx-limited-range not
> being default any more (I cannot remember the bug number which changed
> that though).
>
> Thanks,
> Andrew Pinski
>